class Solution {
public:
    int mySqrt(int x) 
    {
        if (x==0)
           return 0;
        int left=1,right=x;
        while (left < right)
        {
            unsigned long long mid = left + (right - left + 1) / 2;
            if (mid*mid<=x)
                left = mid;
            else
                right = mid - 1;
        }
        return left;
    }
};
